Doctors and unscrupulous agents are signing up immigrants for free NHS treatment despite knowing they have entered Britain illegally.

An undercover investigation by The Sunday Times exposed an agent charging £250 to guarantee a reporter posing as an illegal immigrant a place on a GP’s register. The agent even offered a “buy four, get one free” deal if the reporter could provide her with more clients.

Several doctors agreed to enrol reporters as NHS patients despite being told clearly they were in Britain illegally.

One GP promised to arrange for an illegal immigrant to have a hip replacement operation that would cost more than £13,000 if carried out privately.

The ease with which The Sunday Times was able to register with GPs will fuel concerns that immigrants are being attracted to Britain because of the opportunity to receive free medical treatment.

The investigation also revealed the chaotic rules governing the registration of illegal immigrants by GPs.

The Department of Health, Royal College of General Practitioners, British Medical Association and General Medical Council say such decisions are at the discretion of an individual GP.

Despite that, some primary care trusts which fund GPs have banned doctors from taking on illegal immigrants. Many other GPs have chosen to impose their own ban.

The lack of clarity leaves the taxpayer with a substantial bill, not only to meet the cost of treating those in the country illegally but to fund the doctors themselves, whose pay is, in part, calculated by the number of patients they have on their registers.

The health department is reviewing the guidelines, with the initial findings expected next month.

Yet until unambiguous and consistent guidance is provided, unscrupulous women such as Dipika Patel will continue to exploit the system.

Posing as the friend of an illegal immigrant seeking free NHS treatment, our reporter found Patel, who has two children, at her modest terraced home in Forest Gate, east London, where she boasted of helping dozens of illegal immigrants to enrol with GPs.

Patel explained how she passed the details of men and women who had entered Britain illegally to Nur Begum, a practice nurse at the nearby Boleyn Road and Sinha medical teaching practices.

Begum, she said, then registered the illegal immigrants despite both practices insisting they had imposed a ban on enrolling such patients.

“It’s best to join the NHS,” Patel said. “If you join the NHS it’s really beneficial . . . The NHS medical card will arrive at this [Patel’s] address. Will he [the illegal immigrant] be able to pick it up from this address? I don’t want him to say that he didn’t receive the NHS card and he lost his money. I don’t want him on my case saying I didn’t deliver.”

Originally from India but granted asylum to stay in Britain, Patel said she had operated the scam for seven years.

After demanding a payment of £250, including her own £100 “administration fee”, she then offered the reporter a “buy four, get one free” deal on registering illegal immigrants with a GP.

“If you bring me three more NHS clients like this guy, then I’ll do one free for you. If you bring people, you can have commission too,” she said, adding that she had previously helped “28 to 30” illegal immigrants to register for free healthcare.

Describing how some of those she had assisted had gone on to receive extensive free treatment in NHS hospitals, Patel added: “This woman was lying in the hospital bed and said to me, ‘You have put me on the NHS. Are you sure I won’t get billed for this?’ I said, ‘Lie down, relax, you won’t get any bill’ . . . There is another girl . . . her husband had a free operation. That operation would have cost thousands of pounds but he got it done for free. It was done on the NHS.”

As Patel promised, Begum called our reporter within hours to confirm that she had arranged his enrolment at the Sinha medical teaching practice in Plaistow, east London, and to arrange an appointment for a check-up. The registration contradicts the policies of both the Boleyn Road and Sinha surgeries. Receptionists at both told reporters last week they could not accept patients unable to provide evidence that they were in Britain legally.

Despite that, Begum welcomed the reporters, posing as the illegal immigrant and his friend. After ushering them into her office, she said: “Now he’s registered as a patient. He can come to see a doctor. Nobody will ask him who registered him.”

She then handed over a pathology test request form and told our reporter to attend a nearby health centre for a blood test, which would cost up to £200 if carried out privately.

When challenged about her activities, Patel swore down the phone before hanging up. Begum did not respond to several requests for comment. There is no suggestion that the doctors or any other members of staff at either surgery are aware of or are involved in the enrolment of illegal immigrants.

However, Dr Virendra Mittal turns a blind eye to the signing up of illegal immigrants despite his surgery in Balham, southwest London, insisting it does not do so.

Mittal wrongly told an undercover reporter that the General Medical Council expected doctors to report illegal immigrants seeking to register with them and, as a result, his practice claimed not to.

He initially treated the reporter as a private patient, charging him £30 for a consultation, before agreeing to register him for free NHS healthcare. The reporter had earlier told the doctor he had no legal right to be in Britain.

Mittal admitted he may have other illegal immigrants on his books. “If somebody tells a lie, if somehow he can prove that he is staying here, then I have no problem because these laws and rules have a grey line. Anybody who can provide proof; that’s why I have left this registration issue with the staff, so I am not involved in that,” he said.

One of those who have benefited from Mittal’s approach is Charan Partap Singh, an illegal immigrant who arrived from India on a six-month tourist visa but remained in Britain for four years before returning home. He said: “I paid an agent £100 and he got me onto the books of a doctor in Balham. There were four of us, all living illegally in London, who joined up from the same address.

“One of my friends had a hip replacement operation done. He couldn’t afford the operation back home but managed to get it done free on the NHS.” Several requests to Mittal to comment went unanswered.

At the Fulham Cross medical centre in west London, Dr Zaheer Hussain said that, regardless of their immigration status, his policy was to enrol a patient if they had been Britain for more than six months.

“Some doctors don’t [register illegal immigrants], but we don’t make too many investigations,” he said, before writing out a private prescription for a fictitious stomach complaint.

When the reporter returned four days later, Hussain agreed to prescribe medication to help with heartburn on the NHS.

He said: “We’ve applied for your national health [registration]. It hasn’t come through yet but I’ll give it to you on that. This medicine is £28, the other one [the earlier private prescription] was £3 . . . GPs don’t normally give this medicine, you get it in hospitals. It’s 10 times more expensive than the other one I gave you. They are both the same thing.”

When another undercover reporter visited the surgery and told Hussain that a female relative, also living illegally in Britain, needed a hip replacement operation, he replied: “It’ll be all done [sic]. I can’t do it but I can refer her. Just tell her to make an appointment . . . Believe me, she will be treated just as everyone else here who has a right. She’ll be seen here as another patient.

“Nobody will ask her when she came, why she came. There will be no checks [at the hospital]. They will check through us. Once you get a 10-digit registration number . . . I need that number to send someone to hospital otherwise they will charge her.” A hip replacement carried out privately would cost around £13,000.

Confronted about his comments, Hussain said: “There is a need for clear guidelines on this issue. I was under the impression that anyone who has been here for more than six months was eligible for NHS treatment.”

The General Medical Council said it would examine the findings of our investigation. “Our guidance makes clear that doctors must be honest and act with integrity, which is at the heart of medical professionalism. Serious or persistent failure to follow this guidance will put a doctor’s registration at risk,” it said.